This invention relates to a material for thick film resistor for thermal head, a thick film resistor for thermal head obtained therefrom, and a thermal head obtained by coating the material for thick film resistor on a substrate and a thermal head calcining, and suitable for thermal printing with high image quality.
Materials for thick film resistors constituting thick film thermal heads have heretofore aimed at improving breakdown power characteristics and stabilizing the resistance values during operation as disclosed, for example, in Japanese Patent Examined Publication No. 56-13629, or aimed at improving the selectivity of the resistance values by heat treating a resistor paste at high temperatures as disclosed, for example, in Japanese Patent Unexamined Publication No. 50-67486.
In other words, the prior art thick film thermal heads have only aimed at reducing the price and maintaining the reliability of the resistors, and ignored the reduction of scattering of resistance values of thermal head required for high image quality. That is, it has not been considered to make the output image high quality by reducing the scattering of resistance values of thick film thermal heads, which have scattering of resistance values of about .+-.20% in terms of the maximum-minimum value width and about 7% in terms of variance. By such scattering, foaming non-uniformity takes place, which results in giving unsatisfactory images.